1. Field of the Invention
This invention relates to a plastic molding method and apparatus and specifically relates to the adjustability of multiple manifolds holding a plurality of plastic injection nozzles for a molding machine.
2. Description of Prior Art
Three major areas of the prior art require discussion in order to understand the need for this invention. Most injection molding machines, and specifically those involved in the injection of foam plastic, are very restricted as to the placement of nozzles which feed plasticized material into the mold cavity. This basic restriction is a carry-over from the injection molding processes and many attempts have been made in the art to reduce this restriction. A specific method is U.S. Pat. No. 3,718,166 which allows a limited universal movement of the nozzle end to accommodate the mold. This method, however, still places a restriction on the mold designer as to the placement of nozzles for injection of plastized material. This restriction, which is accepted industry practice, places the center of the nozzle axis starting from the centerline of the platen on a 6 inch grid spacing in both directions.
In an injection molding process, the material can be forced into all the areas of the mold cavity by high pressure ranging from 2,000 psi to cover 10,000 psi. Hence, the tonnage of the machine and its clamp pressure are directly proportional to the size of the part to be molded. However, in using a foaming plastic, large clamping forces are not needed because a foaming agent or an inert gas, such as nitrogen, is introduced into the plastic material; and, after it is released into the mold cavity, the gas at low pressure ranging from 50 psi to 500 psi in the melt will force the plastic into all the corners and sections of the mold. However, as the gas is expanding in the mold cavity, the plastic material is setting up and beginning to solidify. This means it is not practical, if size is a consideration, to have just one nozzle entering the mold cavity. Therefore, in almost all applications, fixed multiple nozzles such as shown in U.S. Pat. No. 3,718,166 are used in the injection molding of plastic parts and is extended to the injection molding of foam plastic to get the foaming agent and plastic material to all parts of the mold as quickly as possible. This resolved the problem of expanding plastic and distribution but the mold designer was still very restricted on the exact placement of gating into the mold due to fixed nozzle positions. To circumvent this problem, special fixed plates in the mold or machines were made to accommodate the sprue and gate openings in the mold.
The third major item is replacement of heater bands or general maintenance on the nozzles. A typical problem with a structural foam injection molding machine is the breakdown of heater bands on the nozzle. These heater bands must be replaced because, with a nozzle plugged, the distribution of the plastic material will not be uniform in the part being molded. The replacement of the heater bands usually necessitates removing the mold from the fixed clamp plate, a very time consuming job, and stepping inside the machine to make any repair.